Interleukin 1 (IL-1) is a pro-inflammatory cytokine produced mainly by macrophages and monocytes in response to inflammation, infection, and other environmental challenges. At low concentrations, IL-1 functions as a mediator of local inflammation. At higher concentrations, IL-1 enters the blood stream. Systemic IL-1 has the ability to cause fever, to induce synthesis of acute phase plasma proteins by the liver, and to initiate metabolic wasting. Accordingly, it is desirable to have inhibitors that block IL-1 mediated inflammation. Similarly, it is desirable to have inhibitors that block the inflammation induced by tumor-necrosis factor (TNF), a cytokine having functions similar to that of IL-1.
IL-1 elicits most of its biological effects by activating transcription factors such as nuclear factor kappa B (NF.kappa.B), activating transcription factor (ATF) and activator protein(AP1) and thereby inducing the transcription of various genes. The first step in the IL-1 transcription signaling pathway involves binding of IL-1 to a receptor on a target cell. The final step in the IL-1 signaling pathway presumably involves interaction between the transcription activators NF.kappa.B, ATF or AP1 with their respective response elements in the promoters of an IL-1 inducible gene.
A proposed model for the major IL-1 initiated and the TNF-initiated signaling pathways is shown in FIG. 1. Since genetic information about the components of these pathways is largely lacking, it is uncertain if these proposed signaling pathways are complete or whether the proposed order of steps is entirely correct.
Accordingly, it is desirable to have model systems for obtaining genetic information about the IL-1 and TNF signaling pathways. Specifically, it is desirable to have mutant cell lines which, in contrast to their parent cell lines, are unresponsive to IL-1 or TNF. Such mutant cell lines are useful model systems for testing the accuracy of the currently proposed IL-1 and TNF signaling pathways. Such mutant cell lines also allow one to determine whether there are other, as yet unidentified, components in the proposed pathways. Mutant cells that lack a known component of one or more of the proposed pathways are especially desirable. Such cell lines are useful model systems for identifying the regions of the known protein that are essential for the known protein to function as an IL-1 or TNF signaling pathway component. Such information allows one to design molecules which interact with these essential regions and which may be useful for blocking the biological effects of IL-1 and TNF.